RE: [PATCH net-next v5] ethernet: fix PTP_1588_CLOCK dependencies

["Keller, Jacob E" <jacob.e.keller@intel.com>]

> -----Original Message-----
> From: Arnd Bergmann <arnd@kernel.org>
> Sent: Thursday, August 05, 2021 6:32 AM
> To: David S. Miller <davem@davemloft.net>; Jakub Kicinski <kuba@kernel.org>;
> Richard Cochran <richardcochran@gmail.com>
> Cc: Arnd Bergmann <arnd@arndb.de>; Shannon Nelson
> <snelson@pensando.io>; Keller, Jacob E <jacob.e.keller@intel.com>; Andrew
> Lunn <andrew@lunn.ch>; Vladimir Oltean <olteanv@gmail.com>; Claudiu Manoil
> <claudiu.manoil@nxp.com>; Alexandre Belloni
> <alexandre.belloni@bootlin.com>; Yisen Zhuang <yisen.zhuang@huawei.com>;
> Brandeburg, Jesse <jesse.brandeburg@intel.com>; netdev@vger.kernel.org;
> linux-kernel@vger.kernel.org; intel-wired-lan@lists.osuosl.org
> Subject: [PATCH net-next v5] ethernet: fix PTP_1588_CLOCK dependencies
> 
> From: Arnd Bergmann <arnd@arndb.de>
> 
> The 'imply' keyword does not do what most people think it does, it only
> politely asks Kconfig to turn on another symbol, but does not prevent
> it from being disabled manually or built as a loadable module when the
> user is built-in. In the ICE driver, the latter now causes a link failure:
> 
> aarch64-linux-ld: drivers/net/ethernet/intel/ice/ice_main.o: in function
> `ice_eth_ioctl':
> ice_main.c:(.text+0x13b0): undefined reference to `ice_ptp_get_ts_config'
> ice_main.c:(.text+0x13b0): relocation truncated to fit: R_AARCH64_CALL26
> against undefined symbol `ice_ptp_get_ts_config'
> aarch64-linux-ld: ice_main.c:(.text+0x13bc): undefined reference to
> `ice_ptp_set_ts_config'
> ice_main.c:(.text+0x13bc): relocation truncated to fit: R_AARCH64_CALL26
> against undefined symbol `ice_ptp_set_ts_config'
> aarch64-linux-ld: drivers/net/ethernet/intel/ice/ice_main.o: in function
> `ice_prepare_for_reset':
> ice_main.c:(.text+0x31fc): undefined reference to `ice_ptp_release'
> ice_main.c:(.text+0x31fc): relocation truncated to fit: R_AARCH64_CALL26 against
> undefined symbol `ice_ptp_release'
> aarch64-linux-ld: drivers/net/ethernet/intel/ice/ice_main.o: in function
> `ice_rebuild':
> 
> This is a recurring problem in many drivers, and we have discussed
> it several times befores, without reaching a consensus. I'm providing
> a link to the previous email thread for reference, which discusses
> some related problems.
> 
> To solve the dependency issue better than the 'imply' keyword, introduce a
> separate Kconfig symbol "CONFIG_PTP_1588_CLOCK_OPTIONAL" that any driver
> can depend on if it is able to use PTP support when available, but works
> fine without it. Whenever CONFIG_PTP_1588_CLOCK=m, those drivers are
> then prevented from being built-in, the same way as with a 'depends on
> PTP_1588_CLOCK || !PTP_1588_CLOCK' dependency that does the same trick,
> but that can be rather confusing when you first see it.
> 
> Since this should cover the dependencies correctly, the IS_REACHABLE()
> hack in the header is no longer needed now, and can be turned back
> into a normal IS_ENABLED() check. Any driver that gets the dependency
> wrong will now cause a link time failure rather than being unable to use
> PTP support when that is in a loadable module.
> 
> However, the two recently added ptp_get_vclocks_index() and
> ptp_convert_timestamp() interfaces are only called from builtin code with
> ethtool and socket timestamps, so keep the current behavior by stubbing
> those out completely when PTP is in a loadable module. This should be
> addressed properly in a follow-up.
> 
> As Richard suggested, we may want to actually turn PTP support into a
> 'bool' option later on, preventing it from being a loadable module
> altogether, which would be one way to solve the problem with the ethtool
> interface.
> 
> Fixes: 06c16d89d2cb ("ice: register 1588 PTP clock device object for E810 devices")
> Link: https://lore.kernel.org/netdev/20210804121318.337276-1-
> arnd@kernel.org/
> Link:
> https://lore.kernel.org/netdev/CAK8P3a06enZOf=XyZ+zcAwBczv41UuCTz+=0FMf
> 2gBz1_cOnZQ@mail.gmail.com/
> Link: https://lore.kernel.org/netdev/CAK8P3a3=eOxE-K25754+fB_-
> i_0BZzf9a9RfPTX3ppSwu9WZXw@mail.gmail.com/
> Link: https://lore.kernel.org/netdev/20210726084540.3282344-1-
> arnd@kernel.org/
> Acked-by: Shannon Nelson <snelson@pensando.io>
> Acked-by: Jacob Keller <jacob.e.keller@intel.com>
> Acked-by: Richard Cochran <richardcochran@gmail.com>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>


v5 looks great to me.

Thanks,
Jake